Testing capacitor units

Below we discuss briefly recommended tests on a finished capacitor unit based on various lEC recommendations. For standards refer to the list provided at the end of the chapter. 

Routine tests are carried out on each capacitor unit. 

Protection, maintenance and testing of capacitor units 26/839 Table 26.3 Power frequency lest voltages and their duration for voltage tests on a power capacitor unit or bank... 

The above tests refer to dry power frequency voltage withstand tests for indoor units. Outdoor capacitor units will be subjected to a wet test as in lEC 60060-1. 

Every capacitor unit will be subject to an a.c. test at a voltage specified in Table 26.3 at a frequency between 15 and 100 Hz, preferably as close to the rated as possible. During the test no permanent puncture or flashover should occur. 

This is another name for a heat run test. A voltage sufficient to cause an output of the capacitor unit equal to 1.5 times the rated output is applied at the rated frequency and test conducted for at least 48 hours. During the last six hours of the test the temperature rise and tan 5 are measured at least four times. The temperature rise during the last six hours should not exceed 1 C, otherwise the test duration must be extended until the temperature stabilizes to a rise of only l°C. The final test results... 

The lest voltage should be 2.5 V, irrespective of star- or delta-connected units. Tlie capacitor unit should be charged with the test voltage and discharged five times within 10 minutes. Within 5 minutes after the test the unit may be subjected to voltage lest (.3) between the terminals. The... 

One will appreciate that such tests are no guarantee of the minimum life of a capacitor unit. Moreover, it is not expected that such tests can predict the future of the capacitor units. They can, at best, suggest the compliance of the test requirements which should ensure a reasonably prolonged operating life of the capacitors, as envisaged. These tests do provide feedback to the manufacturer on the t uality of the dielectric and the process of insulation adopted and if iiny improvements are required. 

This is an alternative to the ageing test and is applicable for shunt capacitors of 1000 V and above. It is an in-house process test and is carried out on the capacitor elements before they are assembled into a capacitor unit to ascertain their dielectric stability against repeated overvoltages. For the test procedure refer to lEC 60871-2. 

Protection, maintenance and testing of capacitor units 26/843 Current unbalance... 

Protection and safety requirements Installation and maintenance of capacitor units Test requirements... 

CAUTION Devices such as solid-state components, capacitor units or any other devices which are not designed to withstand Megger voltage should be disconnected before testing the rest of the motor control center. 

Additional tests on a capacitor VT The tests discussed above refer generally to the electromagnetic unit only. To test the whole VT, the following tests are recommended. For the test procedure and results refer to lEC 60186. 

Can the dielectric constant (K) of BT with a particle size of less than 200 mn be increased As stated earher in the background section, the K values need to be higher for embedded capacitor apphcations. How does the tetragonality in terms of the c/a ratio of the BT unit cell relate to the K of the particles The K values of BT-08 powders treated chemically were measured for the test specimens of BT-08 powder consolidated by polyvinyl butyral (PVB) binder with silver electrodes and by being placed under a Hewlett-Packard LCR meter. Our preliminary... 

In static renewal tests with embryos and larvae of seven species of fish and amphibians, the toxicity of PCB compounds (i.e.. Capacitor 21, Aroclor 1016, i roclor 1242, Aroclor 1254) was found to increase with percent chlorination 20). The more chlorinated PCBs also exhibit longer environmental half-life (757). The combination of high toxicity and persistence in aquatic ecosystems renders these compounds especially hazardous. Despite curtailment of production in the United States, PCBs still in use or disposed of in recent years continue to pose a problem to water quality. These compounds not only exhibit high toxicity to eggs, embryos, and larvae of aquatic species, but also affect sex hormones and the endocrine mechanisms which regulate reproduction in fish 82). 

The object of the test is to verify that the quality of the insulation is satisfactory and has not deteriorated or short-circuited. The test should be made at the consumer s unit with the mains switch off, all fuses in place and all switches closed. Neon lamps, capacitors and electronic circuits should be disconnected, since they will respectively glow, charge up and be damaged by the test. 

The measured insulation resistance is inversely proportional to the capacitance value of the unit being tested. Insulation resistance is a function of capacitance, and hence minimum standards for insulation resistance in the industry have been established as the product of the resistance and the capacitance, RC. For instance, the minimum RC product for ceramic capacitors must be 1 k 2F when measured at 25 C, and it must be 0.1 k 2F at 125 C. 

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